Or is the ISO performance improved on this body by using DIGIC V+?
It's possible it will help the video out some, simply by being able to process faster and allowing for higher-res recording. I wouldn't expect any big difference in noise performance for video though.
Based on your needs, the video AF could be nice if it actually works. While the 10-20 won't really need it, other lenses can use it. And even with the 10-20, while you're running along with a glidecam, it'd be nice not to have to worry about focusing. Biggest feature for you, if you also take pictures, would be the AF and FPS. Makes it more likely you lock focus and get a cool shot in action.
So if there is no new sensor in terms of quality I am going to get the same as the t2i...
But the most important thing is the image quality!! Surely that should improve in an upgrade..
Would have been nice to see an upgrade sensor, but IQ doesn't mean anything if your shot is out of focus, or you missed the moment. The AF will be a noticeable upgrade from the T3i, and the burst rate will also be a noticeable upgrade. Since many rebel users are people shooting their families and people running around, those are important. And most of them wouldn't notice the difference between an 18mp sensor or a 22mp sensor, except that maybe they'd need a slightly larger hard-drive with the larger sensor